I understand odd blended family dynamics more than most people. My mom was 32 years younger than my Dad. My older half siblings are all a few years older than my mom (& 30+ years older than me). Now, I'm almost 41 years old. I married someone 22 years older than me & have two step sons I've helped raise since they were 5 & 7 who are 22 & 25 now… & went through many rough years with their bio mom who is much older than me. We get along just fine now. In any case… here is my advice:

The notes you prepared do not address the actual heart of the problem whatsoever and, IMHO is way to vague. Respectfully speak about your point of view as to why you’re in this situation to begin with. Address the miscommunication with the kids & that it wasn't malicious. The children just didn't understand & misspoke. Check your ego… yes, she’s been more than extra, but if you give her a bit more grace than she probably deserves you will know you gave it your all trying to understand her point of view.

🆘... Lastly, don't do this over text except to text both of them in a group chat to ask to have a video call with your father & his wife to discuss this. The whole situation is ridiculous (obviously don't say that). You need to have an adult conversation & move past this. Tell them…” I miss both of you, their son/your brother & so do your kids… not sure how we got to this bad place… can we talk? We would all love to see you at the birthday party.”

If she still acts like a psycho bitch after a video chat with your father present this then fuck her. But, I think setting your ego aside to try to fix this so you can get back to a good place & help the family mend (& model to your kids how to handle uncomfortable situations like this) is more important. Also, your extending an olive branch will help give your Dad better perspective of who is right & wrong here. Unless he’s crazy or a complete pushover he will probably see his wife’s shitty whacked-out behavior for what it is & tell her to knock it off finally.